The overall objectives of this proposal are to elucidate the structural and chemical mechanisms responsible for generating regional differences in the function of the plasma membrane of mammalian spermatozoa, to define the mechanisms responsible for the developmental modifications of the sperm membrane which occur during maturation in the epididymis and to determine how these changes relate to the spermatozoon's fertilizing ability. The biochemistry and ultrastructure of the plasma membrane of intact spermatozoa and isolated sperm membrane fractions will be studied with the following specific objectives: 1) The regional differences over the sperm surface in the ultrastructure and distribution of the glycocalyx, intramembranous particles and peripheral proteins will be investigated by thin sectioning, freeze-etching and negative stain electron microscopy; by studying sperm from different levels of the epididymis temporal changes in each of these components during sperm maturation will be elucidated. 2) Isolated membrane fractions will be studied by differential extraction experiments, SDS polyacrylamide gel electrophoresis and ultrastructure to determine the mechanisms responsible for generating ordered domains of membrane structure. 3) The externally disposed plasma membrane proteins of the spermatozoon which are coating proteins and which are integral proteins will be determined by subjecting spermatozoa with radiolabelled membrane proteins to specific extraction protocols and analyzing solubilized and non-solubilized components by SDS electrophoresis. 4) Radiolabelled cauda epididymal plasma will be employed in binding studies to determine which components interact specifically with the sperm surface and to identify receptor sites on the spermatozoon. 5) Monospecific antisera against sperm surface components will be employed to evaluate the role of the components in motility or fertilization. 6) The role of androgens in the past-testicular modification of the sperm surface will be evaluated by enzymatically radiolabelling surface proteins of sperm obtained from androgen-depleted animals.